Snap action mechanism



`July 30, 1946. M. J. CAPARONE SNAP ACTION MECHANISM Filed May :5, 1944 mm m EC my W e 66 62 my /t 64j ma Patented July 30, 1.946

SNAP ACTION MECHANISM Michael J. Caparone, Pasadena, Calif., assignor to Grayson Heat Control, Ltd., Lynwood, Calif., a, corporation of California Application May 3, 1944, Serial No. 533,976

5 Claims.

This invention relates to snap-acting mechanisms and, more particularly, to overcenter spring and lever 'devices for operating valves or switches.

A common form of overcenter snap mechanism embodies a frame` having main and secondary levers fulcrumed therein and connected by a spring in such manner that gradual movement of the main lever carries the spring from side to side of the fulcrum of the secondary lever to produce a snap action therein. The torque required merely to overcome friction and inertia of the secondary lever at the beginning of the snap action is insufficient to permit this lever to exert any appreciable force. It is only after the snapaction has progressed sufficiently to increase the torque that the secondary lever can perform useful work. The necessity for such travel on the part of the secondary lever to increase the torque magnitude reduces the force of the snap action and limits the power and. usefulness of such devices for various applications,

An object of this invention is to cause the snap mechanism to exert its maximum force at the instant that snap movement occurs.

Another object of the invention is to utilize substantially the full stroke of the secondary lever to perform useful work.

Another object of the invention is to retain the simplicity of existing snap mechanisms while improving the action thereof.

Another object of the invention is to render the magnitude of the force exerted by the snap lever either variable or fixed, as desired.

Other objects and advantages will become apparent from the following description taken in connection with the accompanying drawing, wherein Fig. 1 is a front elevation of the improved snap-acting mechanism;

Fig. 2 is a section taken on the line 2 2 of Fig.1;

Fig. 3 is a section similar to Fig. 2 but showing the mechanism in another operating position;

Fig. 4 is a section similar to Fig. 2 but showing the snap mechanism in still another operating position;

Fig. 5 is a section taken on the line 5-5 of Fig- 1.

Referring more particularly to the drawing, the conventional parts of a snap-acting mechanism are shown as comprising a channel-shaped frame I having a pair of spaced slots I2 extending through the bottom wall thereof adjacent the one side wall I4 thereof. The slots I2 are each adapted to receive one of a pair of pro- Y jections I6 formed on a channel-shaped base member I8 which is positioned within the frame I0 and extends substantially parallel with the side wall I4. Preferably, the base member I 8 is supported for rocking movement relative to the frame I4 andy for this purpose, the projections I I3 thereof are provided with. notched portions 20 which bear upon knife-edged portions 22 formed on the adjacent edges of the slots I2. The base member I8 may be adjusted on its bearings by means of a set screw 24 which projects through the side wall I4 of the frame and is movable into engagement with the base IB at a point remote from the projections I6.

A main lever 26 of considerably less width than the width of the frame ID is mounted centrallir thereof and extends from the base I8 to the opposite side wall 28 of the frame I9. A knifeedged portion 30 formed on one end of the main lever .26 cooperates with a V-shaped notch or bearing 32 formed in the side wall 28 approximately midway between the ends thereof The opposite end of the main lever 26 is bent at substantially a right angle to the lever body and projects between the side walls of the base I8 forming a free end movable in an arcuate path. This end has a countersunk opening 34 formed therein and the adjacent edge is suitably notched to provide a suspension point 36 for one end of a tension spring 38 which is hooked therearound.

The opposite end of the spring 38 is hooked around a similar suspension point 40 formed by a countersunk aperture intermediate the ends of a secondary lever 42. The secondary lever 42 is forked between the suspension point 40 and the lower end thereof to provide clearance for the spring 38. The forked ends of the secondary lever 42 are provided with knife edges 44 for cooperation with V-shaped notches or bearings 46 formed in the side walls of the base member I8 approximately midway between the projections IB and the opposite ends. The spring member 38 is normally under tension and serves to force the main lever 26 upwardly against its bearing 32. Preferably, the bearings 32 and 46 for the main and secondary levers are in axial alignment and, in the normal or unoperated position of the snap mechanism shown in Fig. 2, the spring 38 is located on the right-hand side of the centerline of these bearings as viewed in 2.

The free end of the secondary lever 42 opposite the knife-edge 44 is bent substantially perpendicular to the lever body and extends in the opposite direction from the free end of the main lever 26 to form an operating portion 48. The

operated position tion shown in Fig. 4.

operating portion 48 is provided with an aperture 50 through which the knife-edged portion 30 of the main lever freely projects. The operating portion 48 is adapted for operative engagement with the device to be operated, such as a switch or the valve 56 shown in broken linesl in the drawing, As indicated in Fig. 4 the valve 56 is moved off its "seat in response to operation of the snap mechanism and may be returned by action of a spring (not shown). v

The secondary lever 42 is further provided with an elongated aperture 52 overlying and connected to aperture 4l and in axial alignment with an aperture 54 formed in the frame I0. The apertures 52 and 54 are adapted to providefreev access to the main lever 26 from the exterior of the frame IIJ in order thatV gradual'movement may be imparted thereto by suitable means. Such movement may result from pressure applied to the main lever 25 by a control device for the valve or switch to be operated and the broken lines in the drawing are intended to represent the actuating portionor push rod 58 cfa thermostat or other control device suitable for this purpose.

In the operation of the mechanism so far described, the parts are moved from the normal or unoperated position shown in Fig. 2 to thefully shown in Fig. 4 by pressure applied to the main lever 26 by the push rod 58. The valve 56 to be operated is shown in Fig. 2 as being in closed position and the operating end 48 of the secondary lever is shown as slightly spacedtherefrom. Movement of the push rod 58 to the left as viewed in Fig. 2 will cause gradual movement of it pivots in its bearing 32 and the suspension point 36 of the spring 38 will move correspondingly in an arcuate path until it is 'in substantial alignment with the knife-edge 44 of the secondary lever 42. The centerline of this position is designated by the broken line A-A in Fig. 2, it being noted that the secondary lever 42 would not partake of the gradual movement due to the component of force acting to produce a clockwise rotation of lever 42. is aligned with knife-edge 44 the mechanism has reached a dead center position thus placing the parts in substantial equilibrium. Continued preseure applied by the push rod 58 to the main lever 26 will cause the suspension point 36 to travel overcenter to the left across the line A-A. The component of force then tends to produce a counter-clockwise rotation of the secondary lever 42 whereupon the tension spring 38 will snap the operating end 48 of the secondary lever from the dead center position to the fully operated posi- Such snap action causes the valve 56 to be moved off its seat and to remain in such position until the push rod 58 returns to its former position and permits the mechanism to resume the normal position shown in Fig.2.

From the foregoing description of the operation of a conventional snap-acting mechanism, it will be apparent that the operating end 48 of the secondary lever 42 cannot exert sufcient force to overcome the closing spring of valve 55 until the lever has travelled far enough to increase its torque to such magnitude as will serve the purpose. Hence, only a portion of the travel can be utilized to perform useful work. This invention is more particularly directed to increasing the range of snap-action movement of the operating lever 42 in order that maximum force may be delivered thereby for unseating the the main lever 26 to the left as When suspension point 35 fr '58 and the side wall 28 of the frame.

4 valve 56 or for operating a switch or other device in accordance with the movement of the control device as represented by the push rod 58.

To this end, means are provided to apply a restraining force to the secondary lever 42 to prevent any movement thereof until sufficient spring tension has been established to overcome the force exerted by the means. Under such conditions, it will be apparent that the mechanism vcannot attain a condition of substantial equilib- -rium and the dead center position is eliminated. ,In-this embodiment, the means so provided may take the form of a permanent magnet 60 comprising a pair of pole faces 62 connected by a bar portion 64. The magnet 60 is mounted on the frame I0 in any suitable location to exert magnetic force upon the secondary lever 42 and is shown herein as being intermediate the push rod It will be apparent, however, that such location of the magnet 60 may be varied to change the operating force exerted by the secondary lever 42 and that magnets of different size and magnetism may be substituted for the same purpose.

The pole faces 62 may project through apertures 66 formed in the frame I0 at the desired location and a retaining clip 68 of sheet material may extend around the bar portion 64 and through slots provided therefor in the frame I0 and be swaged into close engagement with the frame l0 on the inner wall thereof to secure the magnet in position.

In the operation of the improved snap-action mechanism described, the suspension point 36 must travel overcenter across the line A--A without any movement being imparted to the secondary lever 42 due to the magnetic force of the magnet 6i) acting thereon. The main lever 26 continues to move to the left, as shown in Fig.

3 of the drawing, until suflicient spring tension has been established by such movement relative to the secondary lever 42 to overcome the restraining force of the magnet 60. It is apparent that the total force that can be exerted by the secondary lever 42 at the instant that snap action -occurs is equal to the magnetic force acting on the secondary lever 42. 'In this invention movement of the parts to dead center is prevented and the snap mechanism is enabled to exert its maximum force at the instant that snap action occurs.

As a small gap is provided between the end of the valve 56 and the operating end 4S of the secondary lever 42 prior to snap action, the sudden release of force as described creates a high impact force which is usually sufficient to force the valve off its seat even if it is corroded or stuck thereto. Such impact would of course be equally useful in freeing switch contacts which may have become similarly corroded or stuck in closed position. Moreover, due to the increased force of the snap action provided by this invention the valve 55 could be moved to its seat under the action of a more powerful spring than it is possible to provide for use with snap mechanisms of limited snap movement.

It will be understood that various changes may be made in the arrangement and combination of parts and in the details of construction herein disclosed within the scope of the appended claims without departing from the spirit of the invention.

I claim:

l. Snap-acting mechanism oi the character described comprising in combination, a pair of levers pivotally mounted at opposite ends, a tension spring connecting the free ends of said levers and adapted to establish snap-action thereof in response to overcenter movement relative to said mounting, and means adapted to apply a force for preventing one of said levers from participating in said movement until sufficient spring tension has been established to overcome said force.

2. Snap-acting mechanism of the character described comprising in combination, a pair of levers pivotally mounted at opposite ends, a tension spring connecting the free ends of said levers and adapted to establish snap-action thereof in response to overcenter movement relative to said mounting, and magnetic means for preventing one of said levers from participating in said movement until suilcient spring tension has been established to overcome the force exerted by said means.

3. Snap-acting mechanism of the character described comprising in combination, a pair of levers pivotally mounted at opposite ends in bearings, a tension spring connecting the free ends of said levers on one side of the centerline of said bearings, one said connected end being movable overcenter to establish snap-action in the other, and means adapted to apply a force on the lever having said other connected end for preventing participation thereof in said movement until sunlcient spring tension has been established to overcome said force.

4. Snap-acting mechanism of the character described comprising in combination, a main lever, a. secondary lever, oppositely disposed bearings for pivoting said main and secondary levers at one end thereof, a tension spring connecting the free ends of said levers and being located on one side of the centerline of said bearings, said main lever being adapted upon pivotal movement thereof to travel overcenter and impart snapaction to said secondary lever, and means adapted to exert magnetic force on said secondary lever to prevent pivotal movement thereof until said main lever has travelled overcenter and established suilicient spring tension to overcome said force.

5. Snap-acting mechanism of the character described comprising in combination, a frame having spaced bearings therein, a main lever having one end pivotally mounted in one of said bearings and a free end extending adjacent another said bearing, a secondary lever having one end pivotally mounted in said other bearing and a free end extending adjacent the first one said bearing, a tension spring connecting said free ends and being located on one side of the centerline of said bearings, said levers and spring being so arranged that gradual movement of said main lever in one direction on its pivotal mounting will cause the free end thereof to travel overcenter and impart snap-action to said secondary lever, and a permanent magnet carried by said frame and adapted to exert its magnetic force on said secondary lever during a portion of said main lever travel to restrain said secondary lever from pivotal movement until sufilcient spring tension has been established by said main lever travel to overcome said force.

MICHAEL J. CAPARONE. 

